Hierarchical storage management (HSM) systems allow the managed storage of data files among a variety of media such as magnetic hard disks, magneto-optic disks, and magnetic tape. The various media differ in access time, capacity, and cost. Thus, HSM systems typically are configured such that files that are accessed more frequently or created more recently are stored on "short-term" media having the shortest access time. Short-term media often includes a group of magnetic disks, which may be arranged as a redundant array of independent disks (RAID). Files that are accessed less frequently, created less recently, or have larger sizes are stored on "long-term" media having longer access times and larger storage capacities. Long-term media in an HSM system may include rewritable optical disks and magnetic tape media, which can be arranged in a jukebox of magneto-optical disks or a tape library, respectively.
Existing HSM systems typically allocate individual files across the hierarchy of storage media based on frequency of use, creation date, or file size, as discussed above. Accordingly, HSM systems generally seek to avoid excessive access delays in retrieving information that is likely to be accessed most often or most frequently by users. As new files are generated, the system stores the files on the short-term media using a "best-fit" approach. In this manner, the system distributes files across the short-term media in order to minimize wasted storage space. Thus, each file may be stored on a different medium in order to most efficiently manage storage space.
A central database maintains the storage location of each file within the HSM system. If users do not request a particular file for an extended period of time, the system automatically migrates the corresponding file to the longer-term storage media and updates the file location database. Again, the system distributes the relocated file across the long-term storage media in a manner calculated to minimize wasted storage space. For image files, an HSM system may store a number of copies at different display resolutions and on different media to facilitate identification and retrieval by a user. When a user requests a particular file, the system accesses the database to determine the current location of the file. If the desired files reside on longer-term storage media, the system automatically retrieves the files and moves them to the short-term media. If some of the media is not currently loaded into the longer-term storage device, the system generates a request for personnel to physically locate the media and load it into the storage device.